1. Field of the Invention
The present invention provides a heat sink structure, especially suitable for dissipating heat from semiconductor equipment such as CPUs.
2. Description of the Prior Art
In semiconductor devices such as very large scale integrated circuits, some of the applied electrical power is consumed by the operation of the semiconductor device, but the surplus is emitted as heat from the outside of the device. Since, in integrated circuits, the semiconductors are concentrated in a small area, the generated heat is concentrated at certain points and temperatures will rise at certain parts of the devices. In equipment using CPUs and MPUs, etc., the thermal performance especially affects the reliability and life of these elements. Recently, both the density of integration of CPUs and MPUs, etc. and their processing speed have been increasing rapidly, and this has been accompanied by an increase in the amount of heat generated. To avoid the problems associated with this, it is normal to provide a heat sink for the heat emitting component which dissipates the heat over a wider area and thus prevents the temperature from rising excessively. If the heat dissipation is not sufficient, it's effectiveness is increased by adding fins.
FIG. 8 is a cross sectional diagram showing a conventional heat sink mounted on a CPU or similar semiconductor device. As shown by FIG. 8, a heat radiating plate 53 is arranged on the semiconductor device 51 (CPU, MPU or similar) which is mounted on the surface of wiring board 50, with foil contact sheet 54 arranged between them in order to improve the thermal conductivity. This heat radiating plate 53 is fixed to wiring board 50 using a method such as soldering. The heat sink 55 is arranged on top of that radiating plate 53, where the said heat sink 55 and the radiating plate 53 are separated by the foil contact sheet 54, from each other. The heat radiating plate 53 and the heat sink 55 are securely attached to each other on the thread area 56 raising from the heat radiating plate 53, by fastening with nuts 57, to dissipate the heat and cool the equipment. The foil contact sheets are used to improve the contact between the LSI element and the heat radiating plate, and between the heat radiating plate and the heat sink, but in order to improve the thermal conductivity, the connecting surfaces are often coated with a thermally conductive coating of silicon resin.
Conventionally, this type of heat sink structure 55 was formed by die casting etc. out of aluminum or aluminum alloy or other material having good thermal conductivity, and the fins 58 could be formed by machining and cutting. However, as described above, the increasing chip density and processing speed of electronic components is accompanied by increased generation of heat, and so it is necessary to increase the thermal radiation efficiency of heat sink 55, but unfortunately there is a limit to the amount by which the surface area of fins 58, which act to dissipate the heat of this type of heat sink, can be increased. Also, this structure uses nuts, etc., to mount the heat sink on the LSI element, and said nuts must be tightened or loosened individually when mounting and removing the structure, which creates a requirement for extra labor.